The Racetrack is a unique attraction of Death Valley National Park that not many park visitors get to see. It's a dry lakebed in a very remote and beautiful area. On the north end of the lakebed is a rock formation known as the grandstand. Rocks from the grandstand and other nearby formations break off and fall onto the lake. There, they perform feats that make this remote playa world-famous.
They move! But after all these years, a hundred or more since this phenomenon was brought to the attention of naturalists studying Death Valley, no one has ever seen them move. These rocks aren't boulders; most are perhaps a foot or so tall, but can still weigh a lot and are not easy to lift. (Please don't try - leave the rocks in place for others to enjoy.)
The evidence that they move is the trails they leave behind them as they scoot around the lake. You'll find a rock sitting innocently anywhere on the playa -- from next to the grandstand but mostly at the far southern edge -- and behind it will be a trail, from the rock sliding across the fine clay surface of the lakebed.
When this phenomenon was discovered around 1900, observers speculated that magnetic forces were the cause. Now, however, scientists believe they have solved the mystery of this movement. It occurs, they believe, when there's been enough rain to wet down the lakebed, then a strong wind -- as much as 70 miles per hour in this area -- blows the rocks around. The surface of the lake is a fine clay that becomes extremely slick when wet. But since no one has yet seen them move, this is still just a theory.
The Racetrack is located beyond Ubehebe Crater, which is southwest of Scotty's Castle of Scotty's Castle. Getting there involves a long drive down a severely washboaded dirt road - OK in a passenger car in good conditions, but with a notorious reputation for shredding tires. A more interesting approach is via the Lippincott Mine Road from Saline Valley. Strictly 4wd, and exciting, but not too serious unless there have been recent washouts.
[this description adapted from Len Wilcox]